Conjugated polymers in an arene sandwich

A series of poly(p-arylene butadiynylene)s containing zero, one, and two co-facial pi-pi interactions per repeat unit were synthesized and characterized. A surprisingly selective and high-yielding Diels-Alder cycloaddition of anthracene and nonsymmetric, sterically hindered anhydrides proved essential to generating the cofacial arene-containing monomers. Single-crystal X-ray structures display nearly parallel cofacial arenes that are within the van der Waals contact distances. The precursor molecules with cofacial arenes undergo reversible one- and two-electron oxidations to the radical cation and dication in CH2Cl2. The anhydrides were converted to N-alkyl imides to increase the solubility. High-molecular weight poly(p-arylene butadiynylene)s were prepared via Pd/Cu(I)/benzoquinone oxidative coupling of the diacetylene monomers. The resulting polymers are highly emissive in solution and thin films. The ionization potentials were measured using ultraviolet photoelectron spectroscopy with thin films. Last, fluorescence measurements of polymer thin films during continuous irradiation indicate that the most hindered polymer is more resistant to photobleaching.     

Nucleophilic substitution reactions in chromium arene phosphite dicarbonyl chelate complexes

Conclusions An F atom and PhO group on a coordinated P atom in chromium arene phosphite dicarbonyl chelate complexes undergo nucleophilic substitution when treated with PhLi without ring opening to give the corresponding arene diphenylphosphinite chelates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1900–1902, August, 1981.     

Interrupted nazarov reactions using dichlorocyclopropanes: a novel mode of arene trapping

2-Siloxy-2-alkenyl-1,1-dichlorocyclopropanes with aryl-terminated side chains undergo silver-assisted electrocyclic opening/Nazarov cyclization. The resulting 2-siloxycyclopentenyl cations are intercepted by the pendant arenes to furnish tricyclic adducts in moderate to good yields. In cases where the arene trap was tethered through the cyclopropane unit, a new mode of trapping occurred to generate unique bridged carbon frameworks.     

Asymmetric synthesis of secondary benzylic alcohols via arene chromium tricarbonyl complexes

(Aryl aldehyde)- and (aryl ketone)-chromium tricarbonyl complexes ortho-substituted with the chiral auxiliary O-methyl-N-(α-methylbenzyl)hydroxylamine undergo diastereoselective addition of Grignard reagents and Super-Hydride^®, respectively, to give the corresponding secondary alcohols in high diastereoisomeric purity. These compounds may be easily decomplexed and deprotected to give the corresponding enantiopure amino alcohols.     

PEGylated calix[4]arene as a carrier for a Bodipy-based photosensitizer

Heavy atom substituted Bodipy compounds, unlike the parent chromophore, undergo rapid intersystem crossing to generate singlet oxygen, which is the primary cytotoxic agent exploited in PDT. In this work, we show that an organic soluble calix[4]arene can be functionalized by Knoevenagel reaction and then converted into an amphiphilic photosensitizer in a few steps. In addition to generating a potentially useful photosensitizer, the sequence of reactions is the first use of a Bodipy dye as a chromophoric/fluorogenic label without the typical reactive functional groups.     

Synthesis and reversible thermo-induced conformational transitions of a stable nitroxide biradical based on calix[4]arene

A stable paramagnetic calix[4]arene(III) bearing two nitroxide groups on the upper rim is synthesized, which exhibits a strong intramolecular spin-spin exchange interaction and is found to be able to undergo reversible conformational transitions upon heating.     

Synthesis of arene ruthenium triazolato complexes by cycloaddition of the corresponding arene ruthenium azido complexes with activated alkynes or with fumaronitrile

The neutral arene ruthenium azido complexes [(η⁶-p-cymene)Ru(LL)(N₃)], [LL = acetylacetonato (acac) (4), benzoylacetonato (bzac) (5) diphenylbenzoyl methane (dbzm) (6)] undergo [3+2] cycloaddition reaction with a series of activated alkynes and fumaronitrile to produce the arene ruthenium triazolato complexes: [(η⁶-p-cymene)Ru(LL){N₃C₂(CO₂R)₂}] [LL = (acac), R = Me (7); LL = (bzac), R = Me (8); LL = (dbzm), R = Me (9); LL = (acac), R = Et (10); LL = (bzac), R = Et (11); LL = (dbzm), R = Et (12) and [(η⁶-p-cymene)Ru(LL)(N₃C₂HCN)]; LL = acac (13), bzac (14); dbzm (15). However, cationic azido complexes, [(η⁶-p-cymene)Ru(dppe)(N₃)]⁺ and [(η⁶-p-cymene)Ru(dppm)(N₃)]⁺ do not undergo such cycloaddition reactions. The complexes were characterized on the basis of microanalyses, FT-IR and NMR spectroscopic data. Crystal structures of representative complexes were determined by single crystal X-ray diffraction.     

Novel clicked tetrathiafulvalene-calix[4]arene assemblies:Synthesis and intermolecular electron transfer toward p-chloranil

Two tetrathiafulvalene-calix[4]arene assemblies（TTF-calix-1 and TTF-calix-2） have been synthesized by the click reaction.Both their cyclic voltammograms show,as expected,two one-electron quasi-reversible redox behavior.The UV-vis absorption spectra studies show that these two assemblies undergo progressive oxidation at the TTF moiety in presence of increasing amounts of Cu²⁺ or Hg²⁺. Moreover,the absorption studies show intermolecular electron transfer between compounds TTF-calix- 1 or TTF-calix-2 and p-chloranil may be promoted by specific metal ions such as Pb²⁺,Sc³⁺ etc.     

Intramolecular Pd-catalyzed carbocyclization, Heck reactions, and aryl-radical cyclizations with planar chiral arene tricarbonyl chromium complexes

(o-butenylhalobenzene)Cr(CO)(3) complexes were synthesized by diastereoselectve allylmetal additions to o-halo benzaldehyde complexes. The addition of allylZnBr proved particularly convenient and clean. The complexes undergo intramolecular Pd-catalyzed cyclizations (Heck reactions) without decomplexation and/or alkene isomerization. In complexes with a benzylic stereogenic center, the diastereoselectivity of the alkene carbopalladation is governed by the planar chirality of the complex rather than by the benzylic stereogenic center in the side chain. This reaction outcome can be rationalized by the geometry of the arene plane vs that of the Pd coordination plane in the transition step of the alkene carbopalladation step. An alternative cyclization procedure involves the generation of a Cr(CO)(3)-coordinated arene radical from the bromo and iodo complexes. Intramolecular aryl-radical cyclization affords indan complexes. The transition metal arene pi-bond remains intact during this process.     

The chemistry of polycyclic arene imines. III. N-alkylation of phenanthrene 9,10-imineN-alkylation of phenanthrene 9,10-imine

Phenanthrene 9,10-imine ( 1 ) was shown to undergo N-alkylation without aziridine ring cleavage by (a) metallation with sodium methylsulfinylmethide followed by addition of an alkyl halide at −20° (b) reaction of 1 , sodium hydride and the halide in dimethylformamide at 40° (c) treatment of a dichloromethane solution of 1 , the halide and triethylbenzylammonium chloride with aqueous sodium hydroxide under phase transfer conditions. The syntheses of N-isopropyl-, N-butyl-, N-pentyl-, N-allyl- and N-benzylphenanthrene 9,10-imine ( 2–6 ) are described.     

Insights into DNA binding of ruthenium arene complexes: role of hydrogen bonding and pi stacking

Density functional theory (DFT) methods are used to investigate the binding of ruthenium arene complexes, proposed as promising anticancer drugs, to isolated nucleobases. This shows a clear preference for binding at guanine over any other base and an approximately 100 kJ mol (-1) difference in binding between guanine and adenine in the gas phase, while binding to cytosine and inosine are intermediate in energy between these extremes. Solvation reduces binding energies and the discrimination between bases but maintains the overall pattern of binding. DFT and ab initio data on arene-base interactions in the absence of ruthenium show that stacking and hydrogen-bonding interactions play a significant role but cannot account for all of the energy difference between bases observed. Atoms-in-molecules analysis allows further decomposition of binding energies into contributions from covalent-binding, hydrogen-bonding, and pi-stacking interactions. Larger arenes undergo stabilizing stacking interactions, whereas N-H...X hydrogen bonding is independent of arene. Pairing of guanine to cytosine is affected by ruthenium complexation, with individual hydrogen-bonding energies being altered but the overall pairing energy remaining almost constant.     

Viologen-calix[6]arene pseudorotaxanes. Ion-pair recognition and threading/dethreading molecular motions

A calix[6]arene wheel, whose cavity has been extended and rigidified by N-phenylureido groups on the upper rim, forms pseudorotaxane species with molecular axles containing the viologen (4,4'-bipyridinium) unit in CH(2)Cl(2) solution. In these conditions, the self-assembly process is very efficient, with associated DeltaG degrees values of around -8 kcal mol(-1). The counteranions of the bipyridinium-based threads play indeed an important role in the formation of the complex. The use of either tosylate or hexafluorophosphate salts of the guests affects both the stability of the complexes and the rate of the threading process. Such effects have been interpreted in terms of ion-pair recognition, suggesting that coordination of the counteranions of the viologen thread by the ureido groups of the calixarene wheel is crucial for the breaking of tight ion pairs prior to threading. The rate constants of the threading/dethreading reactions coupled with the redox processes of the viologen unit of the axle have been obtained by means of cyclic voltammetry. The pseudorotaxane species undergo fast dethreading (submicrosecond time scale) on electrochemical reduction of the guest. The heterogeneous electron-transfer kinetics for the reduction of the viologen unit is slowed upon encapsulation into the calixarene cavity.     

Complex formation between aliphatic amines and chromogenic calix[4]arene derivatives studied by FT-IR spectroscopy

Complex formation of two calix[4]arene derivatives - containing two ethoxycarbonylmethoxy groups or a bridge including two carboxamide moieties in the coordination sphere - with aliphatic amines (n-octylamine, OA and triethylamine, TEA) were the subject of FT-IR studies. Two nitrophenyl type auxochromic moieties were also present in both of the ligands. Solvent effects were studied in chloroform, diiodomethane and dichloromethane. Presumably, in these reactions, the reactants undergo phenol-amine type interactions and, simultaneously, coordinative interaction takes place between the carbonyl group of the ligand and the protonated form of the aliphatic amine. Complex formation of calixarene 1a with n-octylamine was complete resulting in drastic changes in the FT-IR spectra. Moreover, the possibility of the formation of a new compound by the reaction between the ester type functionalities and octylamine was precluded. The expected ligand was synthesized and its spectra were compared with those of calixarene 1a. In most of the cases of calixarene 1b, the amide moiety of the carboxamide bridge does not participate in the complex formation with the exception of complexes formed in diiodomethane solution and of the 1b-TEA complex observed in dichloromethane.     

Water‐Soluble Pillar[n]arene Mediated Supramolecular Self‐Assembly: Multi‐Dimensional Morphology Controlled by Host Size

We report tunable supramolecular self‐assemblies formed by water‐soluble pillar[n]arenes ( WPn s, n=5–7) and bipyridinium‐azobenzene guests. Nanoscale or microscale morphology of self‐assemblies in water was controlled by the host size of WPn . Supramolecular self‐assemblies could undergo morphology conversion under irradiation with UV light.     

Primary alkyl fluorides as regioselective alkylating reagents of lithium arene dianions. Easy prediction of regioselectivity by MO calculations on the dianion

Lithium arene dianions derived of polycyclic aromatic hydrocarbons, such as naphthalene, anthracene, phenanthrene, fluoranthene, pyrene, chrysene and binaphtyl react cleanly with n-alkylfluorides to afford regiochemically controlled alkylated dihydroarenes after hydrolysis. These arene dianions can be easily prepared by simple treatment of the arene with lithium in THP. Unlike simple radical coupling, the alkylation of these species with alkyl fluorides apparently goes through a S_N2 transition state, despite the inertness of alkyl fluorides to undergo nucleophilic substitution. It is also atypical for reduced arenes, which tend to give ET reactions with other alkyl halides. Prediction of the regiochemistry was easily conducted by means of MO calculations (PM3) on the dianion, and in all cases were consistent with the experimental.     

Cyclometalated complexes derived from calix[4]arene bisphosphites and their catalytic applications in cross-coupling reactions

Palladium and platinum dichloride complexes of a series of symmetrically and unsymmetrically substituted 25,26;27,28-dibridged p-tert-butyl-calix[4]arene bisphosphites in which two proximal phenolic oxygen atoms of p-tert-butyl- or p-H-calix[4]arene are connected to a P(OR) (R = substituted phenyl) moiety have been synthesized. The palladium dichloride complexes of calix[4]arene bisphosphites bearing sterically bulky aryl substituents undergo cyclometalation by C-C or C-H bond scission. An example of cycloplatinated complex is also reported. The complexes have been characterized by NMR spectroscopic and single crystal X-ray diffraction studies. During crystallization of the palladium dichloride complex of a symmetrically substituted calix[4]arene bisphosphite in dichloromethane, insertion of oxygen occurs into the Pd-P bond to give a P,O-coordinated palladium dichloride complex. The calix[4]arene framework in these bisphosphites and their metal complexes adopt distorted cone conformation; the cone conformation is more flattened in the metal complexes than in the free calix[4]arene bisphosphites. Some of these cyclometalated complexes proved to be active catalysts for Heck and Suzuki C-C cross-coupling reactions but, on an average, the yields are only modest.     

The chemistry of polycyclic arene imines. VII. Reactions of phenanthrene 9,10-imine with aromatic carboxaldehydes,carboxylic acids and acetylenic esters

The reactions of phenanthrene 9,10-imine ( 1 ) with aromatic aldehydes, benzoic acids and acetylenedi-carboxylic esters were investigated. The aldehydes were shown to give 1-[N-(arylmethylidene)-9-phenanthreneamine-10-yl]-1a,9b-dihydrophenanthro[9,10-b]azirine 2. The ‘dimeric’ structure of these products was established by X-ray diffraction analysis. The carboxylic acids proved to form in the presence of dicyclohexylcarbodiimide, N-aroylphenanthrene 9,10-imines 7 , that readily undergo rearrangement to N-aroyl-9-phenanthrenamines 8. Esters of acetylenedicarboxylic acid gave the corresponding esters of (Z)-2-(1a,9b-dihydrophenanthro[9,10-b]azirine-1-yl)-2-butendioic acid 10 .     

Endo-cavity Complexes between Calix[6]arene Dianions and Aliphatic Ammonium Cations: Structure of a Hexylammonium Complex by X-ray Crystallography

The interactions of calix[6]arene and p-tert-butylcalix[6]arene with aliphatic amines in acetonitrile solution were studied by spectrophotometric titrations in the UV region and ¹H NMR spectrometry. Calix[6]arenes can undergo two deprotonations by aliphatic amines and the extent of the second proton transfer is mainly governed by the size of the α-substituent of the amine. ¹H NMR spectra show that the macrocycle adopts a 1,2,3-alternate conformation and that the α-hydrogens of the ammonium ions are shielded by the π-clouds of the aromatic rings. The X-ray crystal structure of the dihexylammonium complex of the p-tert-butylcalix[6]arene dianion, reported here, confirms the 1,2,3-alternate conformation and shows one of the two ammonium moieties encapsulated in the inner cavity of the macrocycle.     

Alkali metal mediated conversion of arene oxides and arene imines into aromatic hydrocarbons

K-Region oxides and imines of phenanthrene, chrysene benz[a]anthracene, and dibenz[a,h]anthracene react in tetrahydrofuran with lithium and sodium to give the parent hydrocarbons. In the presence of excessive metal, the latter are converted into dianions from which the parent compounds can be regenerated upon quenching with oxygen. Metalate derivatives of the oxides and imines are proposed to be the corresponding reaction intermediates in the deoxygenation and deamination processes.     

Synthesis, characterization, and X-ray structural analysis of some half-sandwich ruthenium(II) arene complexes with new N,S-donor Schiff base ligands

A series of cationic, half-sandwich ruthenium complexes with the general formula [(η⁶-arene)RuCl(R¹S-C₆H₄-2-CHNR²)]⁺ (arene = p-cymene or hexamethylbenzene; R¹ = CH₂Ph, ⁱPr, or Et; R² = aryl) have been prepared from the reaction of [(η⁶-arene)RuCl₂]₂ with various N,S-donor Schiff base ligands derived from 2-(alkylthio)benzaldehyde and several primary amines. All of the ruthenium complexes were characterized by IR, ¹H NMR, electrochemistry, and UV/Vis spectroscopies. The p-cymene complexes undergo irreversible oxidations while the hexamethylbenzene complexes undergo quasi-reversible oxidations. The molecular structures of ligand 1a and complexes 4a, 4l, and 5e were determined by X-ray crystallography.